1. Field of the Invention
This invention relates to dynamoelectric machines incorporating an air gap baffle assembly.
2. Description of the Prior Art
As is well known, large dynamoelectric machines, such as turbine generators, generate heat when they are in operation due to the internal losses of the machine. To keep the machine operating within desirable temperature limits, a cooling gas, such as hydrogen, is forced through the machine to carry away the heat that is generated by these losses. Most large dynamoelectric machines have, incorporated in the design, provisions for the necessary blower assemblies, heat exchangers, and passageways to insure adequate circulation of the cooling gas which maintains the temperature of the machine, during operation, within acceptable limits. In order to keep the region of the rotor body and the stator bore cool, (this area being commonly referred to as the air gap, whether or not air is the cooling gas) a fixed amount of cooling gas, e.g., hydrogen, is required to flow axially through the air gap. Since the blower on the dynamoelectric machine operates at a required pressure and associated volumetric flow rate, to insure adequate cooling of the entire machine, the cooling gas flowing through the air gap must be regulated to a predetermined flow rate. The standard means of regulation is to insert a restrictive device or baffle at the entrance of the air gap area. This device must provide a preset controllable entrance area to the air gap with a minimum amount of leakage through secondary passages.
FIGS. 1 and 2 are schematic diagrams of the prior art with FIG. 1 being a partial section view of a stator assembly, the baffle ring, and the rotor. FIG. 2 is an end view of the baffle ring and rotor with the stator removed. In FIG. 1 the portions of the stator assembly 100 that are shown are the end pack 105, finger plate 102 and the coil 103. The prior art baffle ring 104 is seated approximately 1 inch into the bore of the machine where a seal is made between the ring and the stator's end pack 105 with impregnated Dacron felt pad 112. The baffle ring is held in place by inserting under every other coil of the stator winding 103 a resin impregnated Dacron pad 114 and the baffle ring is tied in place by use of rope ties (not shown) which are secured through holes 110. The regulation of gas flow through the air gap is controlled through the use of a neoprene rubber insert seal 108. Because in the installation and removal of the rotor assembly it is necessary to insert tools underneath the rotor, there is a keystone area 107 cut out of the seal 108.
On the previous design as shown in FIGS. 1 and 2, the baffle ring was seated approximately one inch into the bore of the machine where a seal was made between the ring and the stator bore with impregnated Dacron felt pad, as was discussed earlier. Since the quality of the seal depended entirely upon the skill of the workmen, the secondary leakage area was somewhat undeterminable and variable from machine to machine. It was also difficult to assemble the felt and at the same time, hold the baffle ring in the desired axial and radial location.
Another drawback with the prior art design is that the baffle ring covered some of the stator iron, iron that is relatively easily damaged since it is at the end of the stator bore. There are other problems encountered by covering the end pack of the stator assembly. For example, inspection by the use of thermovision is very difficult and also, as dynamoelectric machines have increased in size, it has become necessary to provide radial vents in the first end pack of the stator core for additional cooling. Of course, this is impossible with the prior art baffle ring.
Still another problem with the prior art is that in order to prevent the rubber seal from swelling in the presence of oil vapor, it is necessary that the rubber seal by truly oil-resistant and made out of material such as Viton or fluorosilicone. These grades of rubber are quite expensive.
It is a design criterion that the rotor be accessible for the assembly and disassembly tools. In order to do this, there is a keystone notch 107 at the base of the baffle ring. This means that on machines with large air gaps the entrance area in the region of the keystone opening become so large that the regulation of cooling gas flow becomes practically impossible.